The object of the proposed research is to find and characterize neuronal correlates of a behavioral circadian rhythm. The locomotory circadian rhythm of the giant garden slug Limax maximus will be assayed by placing individual animals into specially constructed plastic "running" wheels. The number of 1/4 wheel revolutions per hour can be used as a measure of the level of activity of the animal. Long-term continuous records (2-3 weeks) of wheel-running activity in constant darkness and at constant temperature (20 degrees C) have shown a rhythm with a period (tau) of about 24 hours in preliminary trials. In future experiments an effort will be made to determine (a) the variation tau with temperature and (b) the extent and direction of the phase shift that can be induced by a temperature "pulse" of 12 hours. Concurrent in vitro studies will be conducted to determine whether the isolated slug central nervous system shows evidence of circadian rhythmicity in its spontaneous neural activity. If a neural rhythm (or rhythms) can be found, the variation or tau with temperature and the nature of temperature-pulse-induced phase shifts will be studied. If it can be shown that both the neural and behavioral rhythms (a) have the same or similar tau's, (b) show the same relationship between tau and temperature and (c) respond with similar phase shifts to temperature pulses, it can be assumed that both the neural and behavioral rhythm are driven by the same circadian oscillator. Moreover, it can be concluded that this biological "clock" resides within the nervous system.